1. Field of the Invention
This invention relates to tools for checking the slack on an automotive air brake. This invention more particularly relates to tools for checking the slack in air brake automotive slack adjusters.
2. Discussion of the Background and Prior Art
A typical foundation air brake used on each wheel, or wheel-pair, of large vehicles such as trucks and buses includes an air chamber rigidly mounted on a non-rotating portion of an axle structure near one of the wheels. A piston within the chamber is moved in one direction by compressed air controlled by a valve operated by the driver of the vehicle to apply the brakes by means of a push rod attached to the piston and connected by a clevis to a lever, called a slack adjuster, mounted on one end of a cam shaft. This movement of the lever transmits torque through the camshaft to rotate an S-shaped cam, or S-cam, rigidly mounted on the other end of the shaft. The S-cam transmits the force through cam-follower rollers supported at the ends of brake shoes to force the brake shoes apart and the brake pads mounted on them against the brake drum to brake the vehicle.
The brake shoes are set to move a certain minimum distance before the pads touch the drums, and this distance constitutes slack in the movement of the slack adjuster lever. As the brake drum and the pads wear, the lever has to move farther to apply the brakes, which increases the range of slack movement. This freedom of motion must be limited so that it does not exceed a certain maximum amount, and for that reason the lever includes means for adjusting its angular setting on the camshaft relative to the orientation of the S-cam. The slack adjuster is not directly affixed to the camshaft but is rotatably mounted on a worm gear that has internal spines mounted on spines on the end of the camshaft to prevent the gear from rotating relative to the shaft. The lever can rotate on the worm gear only to a limited extent within a range determined by the engagement of gear teeth on the outer surface of the gear with a worm mounted in a fixed location within the slack adjuster lever. The worm is rotatable about its own axis, which is perpendicular to the axis of the cam shaft, and it has a polygonal head, which is usually hexagonal but is square on some slack adjusters, and is somewhat accessible from outside the slack adjuster to permit the worm to be rotated on its axis by a socket wrench. Excess slack is taken up by rotating the head to adjust the angle of the lever to the proper position to cause the S-cam to begin to apply pressure to the roller followers after the outer end of the push rod extending from the air chamber has moved only a short distance, typically between ½″ and ¾″ from the position it occupies when the piston is not under pressure from compressed air.
Other slack adjusters are referred to as self-adjusting or automatic because they have sensors that detect the amount of slack and are connected to actuating means in the slack adjusting lever to rotate the worm to take up excess slack. However, even the automatic slack adjusters have provision for some manual check.
The slack in each brake of a vehicle so equipped needs to be checked regularly to be sure that the brake shoes apply balanced pressure on the drums so that they can bring the vehicle to a halt without causing it to swerve or skid as it stops. In organizations that operate fleets of vehicles having air brakes, mechanics are required to inspect the brakes on a regular schedule, but in addition, the drivers are also supposed to check the slack adjusters at the beginning of each day's trip.
Recent state and federal regulations, such as the Department of Transportation's 1198 edict, mandate that all truck drivers must be able to measure the slack in the air brakes of the vehicles they own, operate or drive. Thus the air brakes must be checked daily, and certainly before each trip, to determine if the slack of each air brake assembly is within or exceeds the safe working maximum limits.
In the field relating to air brake slack check tools, it is generally known to provide a tool having fixedly spaced engagement members, which members are positioned for engagement of different but a limited number of slack check surfaces. One such tool is disclosure is U.S. Des. 296,750, granted Jul. 19, 1988 to Hamatani (the “Hamatani tool”). The Hamatani tool required two hands to be operable, one hand engages the handle and the other hand adjusts and sets the position using a wing nut. The Hamatani tool relies on the wing nut to hold the set position when the tool was in use. A present widely used tool, quite similar to the Hamatani tool construction, is the Brake Slack Check OTC 5052 tool, commercially available from OTC a division of SPX Corporation, Owatonna, Minn. (the “OTC tool”). The OTC tool provides a four position construction. The OTC tool, like the Hamatani tool, requires two hands to be operable, and provides a limited range of operable positions. The OTC tool also generally requires a two-person operation; a first person operates the tool while a second person in the cab applies force to the brake to permit the first person to use the tool to check the clearance or slack.
The air brake slack check the art desires a tool, which readily provides sufficient gripping and leverage forces for a broad range of slack adjuster surfaces of diverse models of trucks and buses, and yet is practical in design and construction. The air brake slack check art further desires a tool, as aforesaid, which eliminates the number of hands and operators, and yet provides the necessary slack check leverage. The present invention provides a solution to the foregoing slack check art requirements and needs.
In the field related to pliers, it is generally known to provide pliers that are adjustable. Adjustable pliers are disclosed in U.S. Pat. No. 6,892,609, granted May 17, 2005 to Kuo, U.S. Pat. No. 4,603,607 granted Aug. 5, 1986 to Schaffner et al, U.S. Pat. No. 5,134,908, granted Aug. 4, 1992 to Fisher, and U.S. Pat. No. 4,890,519 granted Jul. 2, 1990 to Le Duc.